High temperature and high humidity release coating for polymer film

ABSTRACT

The present invention relates to a release coating composition that may be applied to a film that may then be used as a substrate useful for applications requiring release for a broad range of temperatures and high humidity conditions, which temperatures may range from about 20° C. to about 210° C. These applications include release substrate used in the manufacture of calendared cured sheet rubber and molding paste composites, such as sheet molding compound (SMC), thick molding compound (TMC), bulk molding compound (BMC) and fiberglass composites. The release coating composition comprises a solution of a hydroxypropyl methylcellulose having hydroxypropyl molar substitution of from 0 to about 0.82. In a preferred form, particulate solids are present in the composition.

RELATED INVENTION

[0001] This application claims the benefit of U.S. Provisional PatentApplication No. 60/219,481 filed Jul. 20, 2000 which is incorporatedherein by reference.

FIELD OF THE INVENTION

[0002] The present invention relates to a release coating compositionthat may be applied to a film that may then be used as a substrateuseful for applications requiring release for a broad range oftemperatures and high humidity conditions, which temperatures may rangefrom about 20° C. to about 210° C. These applications include releasesubstrate used in the manufacture of calendared cured sheet rubber andmolding paste composites, such as sheet molding compound (SMC), thickmolding compound (TMC), bulk molding compound (BMC) and fiberglasscomposites.

BACKGROUND OF THE INVENTION

[0003] In the rubber industry, sheets of cured rubber compound areprepared by a calendaring process. Typically these sheets are from about100 to about 400 feet in length. The uncured rubber sheet is laid onto asupporting interleaf film or sheet and then the two sheets are woundonto a mandrel. The interleaf is usually cellophane or silicon coatedpaper. The interleaf does not melt at the curing temperature andprevents the sheets from fusing with each other during the curingprocess. Sometimes talc or zinc stearate is applied to the interleaf toenhance release of rubber sheets from the interleaf after curing.Subsequently, the roll of rubber and interleaf can be over wound andheld under tension using an over-wrap, which can be any film or clothhaving good tensile properties that tends to shrink at oven curingtemperatures. The cured sheet rubber may be used as components foraircraft engines and gaskets for rubber roofing membranes. Teflon®sheets, talc dust, and cloth are commonly used as interleaves in therubber industry.

[0004] SMC is a composite material and usually comprises crosslinkablepolymeric resin, most often unsaturated polyester resin; styrenemonomer, plus catalyst; particulate filler, such as calcium carbonate;chopped glass fiber reinforcement; and various other additives in minoramounts, such as pigments and other modifiers.

[0005] The manufacture of SMC begins by laying the paste comprising allingredients except the glass fibers, on a bottom carrier or releasesheet, i.e., a film. The glass fibers are poured on top of the resin.More paste is poured over the glass fibers. A top carrier release sheetis laid down, and the edges of the top and bottom sheets are folded overto form a sandwich. The film and hence the composite is then kneaded tomix the glass fibers and the paste. The sandwich is then festooned(folded back and forth in a continuous fashion) into a bin and storedfor up to about 14 days to cure or mature. Satisfactory results may beobtainable after as little as 2.5 days, but often more time is required.During this time the viscosity of the composite increases significantly(approximately ten-fold).

[0006] At the end of the curing period, the carrier release films, topand bottom are stripped away, the solidified SMC is cut and put into aheated press. In roughly one minute or less, out comes a semi-finishedproduct, such as an auto part, for example, an automobile hood.

[0007] TMC is produced by a different machine and a process differentfrom those used for producing SMC. Although TMC is prepared as acontinuous length of material, it is cut into slabs for curing andstorage because it is thicker than SMC. SMC is usually 1″ thick, but mayrange from ¼″ to 3″ in thickness. TMC may range from ½″ to 4″ inthickness. TMC is stronger because some of its fiberglass fibers may bepositioned vertically, and more filler may be added. A most significantdifference between SMC and TMC is that in making TMC, the glass fibersare mixed with the paste prior to being deposited on the carrier orrelease film, and thus no kneading of the composite sandwich isnecessary when TMC is made into slabs. This therefore places differentrequirements on the carrier or release film as tear strength may not beas critical for carrier release film used to make TMC.

[0008] BMC is also a composite material of resins, fillers andreinforcements. Typically, it comprises 30% resins, 50% fillers andadditives and 20% reinforcement, such as glass fiber. It may alsocontain catalysts. The high filler loadings can provide improvedstiffness and fire retardence. BMC is manufactured by preparing aputty-like molding compound comprising the above-noted components in a“ready to mold” form. Molding pressures usually range from about 350 to2000 psi at temperatures of between 250 and 350° F. BMC can be made intoprecise shapes with various types of inserts, and therefore the moldingscan be extremely complex. One limitation of BMC is the loss of strengthcaused by degradation of glass fiber reinforcements duringenergy-intensive mixing.

[0009] BMC is primarily used as a replacement for cast metals. Theactual physical characteristics of BMC are determined primarily by thechoice of resin and desired end use. Possible end uses includeelectrical grade; low shrink/general purpose; appliance/structural; lowprofile; automotive grade; and corrosion resistant. Major applicationsof BMC include air conditioner components; pump housings; circuitbreakers; computer and business equipment components; garbage disposalhousings; motor parts; power tools; gear cases; electrical insulators;and circuit covers.

[0010] In selecting a carrier release film there are some basicrequirements or properties that are preferably met for the film to besuitable. While styrene barrier, moisture barrier, and mechanicalstrength are relevant, most important are release from the pastecomposite, be it SMC, BMC, or TMC, and the cost of the release film.

[0011] Nylon films represent a potential replacement for silicon-coatedpaper and cellophane as interleaves in the rubber calendaring industry,because of their high tensile strength. However, the tendency ofcurrently manufactured nylon films to stick to rubber compounds bothcured and uncured limits their use in a rubber release application.Apart from sticking to the sheets of rubber, the latter film sometimescauses wrinkles on the surface of the cured rubber. It is speculatedthat gases emanated during curing of rubber cause such wrinkles.

[0012] Cellulose ethers are water-soluble polymers derived fromcellulose. A commercially available cellulose ether is available underthe Methocel® brand from The Dow Chemical Company. These products areavailable in various viscosity grades, ranging from 3 to over 200,000mPa's. Generally, these viscosities refer to the viscosity of a 2%Methocel® solution in water at 25° C. The methylcellulose productsinclude hydroxypropyl substituted cellulose ethers. Such products arealso available from other sources such as China Yixing Kaili ChemicalPharmaceutical Factory of Yixing city, Jiangsu, China; Carbomer Inc ofWestborough, Mass.; and Penta Mnfg. Co. of Livingston, N.J. Methocel®products are used as mold-release agents, stabilizers, and thickeners inrubber latexes, where they contribute also to more uniform drying andless pinholing (see Dow METHOCEL® Cellulose Ethers Technical Handbookavailable from The Dow Chemical Company Website, July 2000).

BACKGROUND ART

[0013] Various attempts have been made to make and coat non-stickcoatings to film or film structures used for high temperatureapplications. Some of the prior art patents pertaining to releasecoatings are summarized hereafter:

[0014] U.S. Pat. No. 5,139,835 to Kitamura et al discloses a syntheticresin laminated paper which makes it possible to recover paper (orlaminated film) materials easily and rationally. The adhesion-releasecontrol agent layer interposed between the polyethylene film and paperlayer can be polyvinyl alcohol, silicone based compound, or a reactionproduct of an organopolysiloxane compound having at least one doublebond which has reacted with said hydrogen atom.

[0015] U.S. Pat. No. 3,503,773 to Bisschops et al discloses a processfor forming films or foils using a high-gloss-surface or the “castinglayer”. The film-forming polymer solution is applied to the castinglayer and at the end of the process the polymer film is stripped off thecasting layer. The casting layer is a mixture of cellulose acetate andWerner chromium complex salt.

[0016] U.S. Pat. No. 4,956,233 to Chu et al discloses a slip-coatedthermoplastic film having good antiblocking properties. The slip coatingcomprises of an aqueous wax emulsion or dispersion and a minor amount oftalc, syloid or amorphous silica gel.

[0017] U.S. Pat. No. 4,956,241 to Chu et al discloses a slip-coatedbiaxially oriented film having good antiblocking properties. The slipcoating comprises of (a) an aqueous wax emulsion or dispersion, (b) anaqueous polymer solution or emulsion with T_(g) between 30°-100° C., and(c) a minute amount of talc or syloid.

[0018] U.S. Pat. No. 3,945,404 to Yamamatsu et al discloses a foodcasing having the inner surface thereof coated with a water-solublechromium complex to enhance the release of processed meat from thecasing.

[0019] U.S. Pat. No. 5,547,738 to Mitchell et al discloses liner lesslabels where the substrate has a pressure sensitive adhesive on one faceand a release coating on the other. The preferred release coatings areformulations, which include silicone resins and chrome complexes offatty acids.

[0020] U.S. Pat. No. 5,492,599 discloses a treated cellulose-basedsubstrate e.g. paper with good release properties. The treated substrateis coated with a primer coating comprising a cationic polymer and with arelease coating comprising a carboxy- or carboxylate-containing releasepolymer.

[0021] U.S. Pat. No. 2,273,040 describes Quilon®, Werner-type chromecomplexes useful for making a variety of substrates hydrophobic,oleophilic, and softer.

[0022] U.S. Pat. No. 3,484,271 to Kaliski et al describes a two-stepprocess where a polyfunctional anionic component is applied followed bytreatment with a polyfunctional cationic component (Quilon® ChromeComplex) to yield a surface adhesive to cooked food and plastic masses.

[0023] Japanese Examined Patent Application 63,075,199 (Kanzaki Paper)describes a water-soluble copolymer release agent for paper, with Tg of60-20° C., consisting of (a) 5 to 50% of a hydrophilic ethylenicallyunsaturated monomer, e.g., (meth)acrylic acid or maleic acid, (b) 20 to95% of a (meth)acrylate monomer having 4-10 carbons, e.g. butyl orhexyl, and (c) 0 to 40% of another copolymerizable monomer, e.g. vinylacetate, styrene or acrylonitrile. The release paper has excellentthreading and release properties.

[0024] U.S. Pat. No. 4,226,749 describes a sizing composition with acationic and anionic component mixture in a clay coating formulation.

[0025] U.S. Pat. No. 3,976,490 describes topical coating comprising aparticulate material e.g. silica, CaCO₃ in a polymeric binder adhered tothe opaque plastomeric sheet material. The size of the particles and thethickness of the binder are selected to provide for the protuberance ofat least a portion of the particles to act as spacers and thus functionas the primary antiblocking component.

[0026] U.S. Pat. No. 5,959,031 issued to Thurgood Sep. 28, 1999describes a polyamide film forming resin and at least one release agentmaterial selected from the group consisting of N, N′ ethylene bis amidesof the formula R₁—CO—NH—CH₂—CH₂—NH—CO—R₂ wherein R₁ is an aliphatichydrocarbon chain of about 14 to about 42 carbon atoms, and R₂ is ahydrogen atom or an aliphatic hydrocarbon chain of about 14 to about 42carbon atoms, wherein the release agent material is present in an amountsuch that after the paste composite is formed, substantially all of thefilm can be removed from the surface of the composite.

[0027] U.S. Pat. No. 3,837,375 to Higgins et al describes a containerused for packaging viscous tacky polymers by the process of hot filling.The latter containers have an inner lining of heat stabilized nyloncoated with a silicone release agent; an uncoated cellophane film; amineral pigment coated kraft paper overcoated with a silicone releaseagent; or kraft paper coated with finely divided mica. These containersare able to withstand hot packaging temperatures up to 450° F. and atthe same time permit the contents to be readily removed.

[0028] European Patent EP 0295375A2 discloses a silicone coated releasefilm used in film impregnation of cyanate resin based prepegs in acontinuous process. The release film is stripped from the advancingimpregnated film while simultaneously one or more new release films areapplied to the prepeg before, during or after impregnation. Apparently,the silicone coated release papers showed better release than thosecoated with QUILON® in the temperature range of 125° C. -300° C.

[0029] U.S. Pat. No. 5,858,487 to Boehler et al discloses a six layermicrowaveable food wrap where the top layer is a non-stick coating foruse in preventing food from adhering to a polymeric layer. The non-stickcoating is made from a chrome complex of stearic acid ((chromium,pentahydroxy, (tetradecanoata)di-)), and is commercially available fromE.I. du Pont de Nemours and Company as QUILON® C complex (both methylcellulose and hydroxypropyl methylcellulose are recognized as acceptablefood additives by the US Drug Administration (FDA) and are listed in thefood chemicals codex alimentarius (Dow's product literature)).

[0030] U.S. Pat. No. 4,735,860 discloses a heat transfer sheet, whichprevents sticking and blocking problems and makes it possible to carryout printing smoothly. The latter sheet has hot-melt ink layer or oneside and heat-resistant protective layer on the other. Theheat-resistant protective layer comprises (a) thermoplastic resin havinga COOH or OH group, (b) a polyamine or polyisocyanate, and a (c) athermoplastic resin, or a composition based on a silicone-modifiedresin.

[0031] The various types of release materials can be categorized aswaxes, such as petroleum waxes, vegetable waxes, animal waxes, andsynthetic waxes; fatty acid metal soaps, such as metal stearates andothers, for example, calcium ricinoleate; other long chain alkylderivatives, fatty esters, fatty amides and amines, fatty acids andalcohols; polymers, such as polyolefins, silicones, fluoropolymers,natural polymers; others like poly(vinyl alcohol) and polyoxyalkylenes;fluorinated compounds and fluorinated fatty acids; and inorganicmaterials, such as silicates, talc, clays, kaolin, mica, and otherparticulates such as silica, graphite and carbon.

[0032] While all of the above references propose release coatings ofvarious types, there remains a need for effective, inexpensive, hightemperature, high humidity release coatings which can be applied tothermally resistant polymer films and which do not permanently transferoff the film to the surface in contact therewith.

[0033] Traditional release agents such as erucamide andpolytetrafluoroethylene, which bloom to the surface in polyolefins, failto do so in case of nylon films, such as polyamide66. Apparently,polyamide66 films have higher surface tension (43-50dyn/cm), can absorbup to 2% by weight of water and can be heated up to 150° C. with nodegradation. All these properties make polyamide66 film a friendlysubstrate for coating with water based coatings.

[0034] The disclosures of all documents, patents and applicationsreferred to herein are incorporated herein by reference.

SUMMARY OF THE INVENTION

[0035] The present invention provides in a first aspect a coatingcomposition for use as a surface coating for polymer release films foruse in high temperature and/or high humidity applications, whichcomprises a solution of at least one hydroxypropyl methylcellulosehaving hydroxypropyl molar substitution of from 0 to about 0.82.

[0036] In another aspect, the invention provides a release coatingcomposition as defined above, wherein the solution comprises from about0.2% to about 40% by weight, preferably from about 0.2% by weight toabout 15% by weight of low viscosity hydroxypropyl methylcellulosehaving hydroxypropyl molar substitution of from 0 to about 0.82 inwater, wherein low viscosity means the viscosity of a 2% by weight of asolution of hydroxypropyl methylcellulose in water is up to 100centipoise at room temperature (20° C.). The hydroxypropylmethylcellulose is infinitely soluble in water and the maximum amount isdetermined by the coating equipment and cost limitations.

[0037] In another aspect, the invention provides a release coatingcomposition as defined above, wherein the solution comprises up to about3% by weight of high viscosity hydroxypropyl methylcellulose havinghydroxypropyl molar substitution of from 0 to about 0.82 in water,wherein high viscosity means the viscosity of a 2% by weight of asolution of hydroxypropyl methylcellulose in water is from 100 to100,000 centipoise at room temperature (20° C.).

[0038] In another aspect, the invention provides a process for coatingthe surface of a polymer film to provide a release film for use in hightemperature and/or high humidity conditions, which comprises coating atleast one surface of the polymer film with a solution of a hydroxypropyl methyl cellulose having hydroxypropyl molar substitution of from0 to about 0.82 to provide a coating weight of at least about 0.004lb/ream per side and drying the coated film to set the coating. Inanother embodiment of this process, the film is coated on both sides inseparate passes or in a single pass to achieve the desired coatingweight.

[0039] In yet another aspect, the invention provides a release polymerfilm coated on at least one surface with hydroxypropyl methyl cellulosehaving hydroxypropyl molar substitution of from 0 to about 0.82. Therelease film may also be coated with a mixture of the hydroxypropylmethylcellulose having hydroxypropyl molar substitution of from 0 toabout 0.82 and particulate solids.

[0040] The release coating of the present invention has been found to beuseful in cured rubber manufacturing applications and also has utilityin the manufacture of SMC, BMC and TMC, as well as fiberglasscomposites. In addition, it is useful in applications such as thosedescribed in U.S. Pat. No. 3,837,375 (packaging of hot, highly viscous,tacky polymers such as low molecular weight polystyrene); U S. Pat. No.5,858,487 (laminated, non-stick food wraps); and U.S. Pat. No. 4,735,860(therma-sensitive transfer sheets); as well as EP 0 295 375 (cyanateresin-based prepregs and films for use in advanced structuralmaterials).

[0041] In another aspect the invention provides a process for curingrubber which comprises forming a sheet rubber layer in a calendar,laying layers of a release film as described above between layers of thesheet rubber, tightly overwrapping the stack of layers with a releasefilm or cloth, before subjecting the stack of layers to elevatedtemperature in a dry or steam oven wherein the sheet rubber or sheetmolding compound is cured and subsequently unwrapping the stacked, curedsheets.

[0042] In another aspect the invention provides a process for producingsheet molding composites which comprises:

[0043] (a) casting a layer of heat-curable thermosetting resin, in fluidform, onto a continuously advancing polymeric release film;

[0044] (b) introducing reinforcing material onto the advancing fluidlayer;

[0045] (c) laying a polymeric film on the top surface of said reinforcedfluid layer thereby forming a sandwich composite;

[0046] (d) advancing said sandwich composite through a series ofkneading and compaction rolls; and

[0047] (e) winding the sandwiched composite into a roll for partialcuring;

[0048] the improvement comprising using a release film as defined above.In a variant of this process a particulate solid is also present in therelease coating composition.

[0049] In another aspect the invention provides a process for makingthick molding composites, comprising

[0050] (a) introducing reinforcing material into a heat-curablethermosetting resin, in fluid form and mixing same until the material ismixed and wetted;

[0051] (b) casting a layer of said mixture onto a continuously advancingpolymeric film;

[0052] (c) laying a polymeric film on the top surface of saidreinforcing material-resin layer to form a sandwich composite;

[0053] (d) advancing the sandwich composite through at least onecompaction roll;

[0054] (e) cutting the continuous lengths of the sandwich composite intolengths for partial curing;

[0055] the improvement comprising using a release film as defined above.Again, the release composition may also include a particulate solid.

DETAILED DESCRIPTION OF THE INVENTION

[0056] In the following Table 1 there is set out the hydroxypropyl molarsubstitution of various grades of hydroxypropyl methylcelluloseavailable commercially from the Dow Chemical Company, which have beenfound to be useful in the present invention. TABLE 1 DIFFERENT GRADES OFHYDROXYPROPYL METHYL CELLULOSE Hydroxypropyl molar Product substitutionMethocel ®A 0 Methocel ® E 0.23 Methocel ® F 0.13 Methocel ® J 0.82Methocel ® K 0.21

[0057] The degree of hydroxypropyl substitution affects the viscosity ofthe methyl cellulose. Hydroxypropyl methyl cellulose grades can beclassified into high viscosity and low viscosity grades. Low viscositygrades of hydroxypropyl methyl cellulose are those grades, which atsolution concentration of about 2% in water at room temperature (20° C.)result in the solution viscosity in the range of 0.1-100 centipoise.High viscosity grades of hydroxypropyl methyl cellulose are thosegrades, which at solution concentration of about 2% in water at roomtemperature (20° C.) result in the solution viscosity in the range of100-100,000 centipoise. The useful amounts for coating solutions ofhydroxypropyl methylcellulose for use in the present invention rangefrom about 0.2% to about 40% by weight, preferably from about 0.2% up toabout 15% by weight. A most preferred range is from about 0.2 to about6.0% by weight hydroxypropyl methylcellulose in water. The solutions ofsurface treated grades of hydroxypropyl methylcellulose available fromDow Chemical Company in water require pH adjustment in order to triggerthe hydration process and subsequently, the viscosity build up. Thelatter trigger can be conveniently achieved by adding a small amount ofbase, such as ammonium hydroxide to the dispersion of surface treatedhydroxypropyl methylcellulose in water.

[0058] The coating of the methylcellulose solution can be performed byrolling, dipping or spraying. The rolling method is preferred. Detailsof these coating methods are well known to those skilled in the art.Drying of the coated film is preferably by air drying, in a heated oven,at a temperature in the range of about 40° C. to about 120° C.

[0059] The humidity conditions under which the release film performsrange from 0 to about 100% relative humidity. The high temperatureconditions range from about room temperature (20° C.) to about 210° C.

[0060] The solution of methylcellulose may comprise a binary mixture ofan organic solvent and water. Generally such a mixture preferablycomprises about 2 to about 8 parts solvent per one part methylcellulose.An example of a preferred binary solution comprises from 0 to 35% byweight of alcohol, from about 0.2% to about 40% by weight ofhydroxypropyl methylcellulose, and the remainder up to 100% by weight ofwater. There are a variety of organic solvents that may be used in sucha binary mixture and the organic solvent may be selected from glycols,esters and amines. The Dow Technical Handbook for Methocel CelluloseEthers referenced earlier contains a listing of suitable specificsolvents. The solution may be prepared in concentrated form and thendiluted to an appropriate concentration for the desired coating weight.

[0061] The methylcellulose solution may also contain particulate solidssuch as those mentioned above. Preferred are silica and talc. The ratioof particulate solid to methylcellulose is preferably in the range offrom about 0.01 to about 1.5. The amount of organic solvent may range inthis case up to about 50% by weight. The silica may be commerciallyavailable colloidal silica, examples of which are sold under thetrade-marks Ludox®, Bindzil® and Nyacol®.

[0062] While the particulate solids act as processing aids, it has alsobeen recognized that they facilitate higher transfer of the coatingsolution to the film. As a result when the particulate solid is presentin the dried coating and in the preferred amount of from about 0.01 toabout 0.60 by weight fraction, the amount of release agent required,namely the methylcellulose is reduced.

[0063] As is apparent from the subsequent Examples 12 to 16, a solutioncontaining hydroxypropyl methyl cellulose and silica, for example,Methocel® E15LV/Ludox® CL-P ratio equal to 3/1, where Methocel® E15LVaccounts for 1.86% to 3% of the solution, gives surprisingly highertransfer of the coating to a polymer film, such as Dartek® T404 above 2%total solid content of the solution. The latter effect viz. highertransfer of coating to the polymer film at 2% and the above total solidscontent in the solution can be seen in FIG. 4. Ludox® CL-P is an aqueouscolloidal dispersion of 40% by weight of very small silica particleshaving 22 nm average particle diameter. The silica used in Ludox® CL-Pis made up of negative silica particles with a positive layer ofalumina. It is speculated that the positive charge imparted to thecoatings of the invention by the Ludox® CL-P helps the transfer of therelease coating onto the Dartek® T404 film, which has amide negativeions on the surface. For a particular coat weight of a two side coatedDartek® T404 film, 0.01-0.60 weight fraction of silica in the driedcoating reduces the peel strength. The minimum in peel strength is foundaround 0.15 silica weight fraction. However, an excess amount of silica(above 0.60 weight fraction) on the surface increases the peel strengthwith complete adhesion (peel strength of 2000 g/1.27 cm from Viton®rubber compound) at 100% silica in the dried coating. The latter trendcan be seen in FIG. 5.

[0064] The polymer film may be selected from polyolefins, polyesters,nylons and blends thereof. Nylon 66, Nylon 6 and polyester films arepreferred. The films may be monoaxially or biaxially oriented. Generallyany film having a softening point above the temperature of theapplication for the coating may be used. A preferred film is monoaxiallyoriented (in the machine direction) nylon, in particular nylon 66. Acommercial example is Dartek T404 available from Enhance PackagingTechnologies Inc. This film has good MD shrink properties at rubbercuring conditions.

BRIEF DESCRIPTION OF THE DRAWINGS

[0065] In the accompanying drawings which are used to illustrate thepresent invention,

[0066]FIG. 1 is a plot of Peel Strength v. Coat Weight comparing aconventional release coating with the coating of the present invention;

[0067]FIG. 2a is a graphical representation of the effect of varyingmolar hydroxypropyl substitution in hydroxypropyl methylcellulose coatedDartek® T404 (coating of the invention) on peel strength in a wetrelease test with Viton® rubber compound. The solid line contoursrepresent the peel strength in g/1.27 cm;

[0068]FIG. 2b is a graphical representation of the effect of varyingmolar hydroxypropyl substitution in hydroxypropyl methylcellulose coatedDartek® T404 (coating of the invention) on peel strength in a dryrelease test with Viton® rubber compound. The solid line contoursrepresent the peel strength in g/1.27 cm;

[0069]FIG. 3 is a graphical representation of the effect of varyingmolar hydroxypropyl substitution in hydroxypropyl methylcellulose coatedDartek® T404 (both sides) (coating of the invention) on haze after a wetrelease test. The solid line contours represent lines of constantpercent haze;

[0070]FIG. 4 is a graphical representation of the coat weight using avariety of coatings, including those of the invention obtained onDartek® T404 on a Faustel coater using 165 quad cylinder, as a functionof percent solids in the water plus isopropanol solution;

[0071]FIG. 5 is a graphical representation of the effect of increasingthe weight fraction of silica in a dried coating, on a two side coatedDartek® T404 film, on the release performance in a dry release test. Thelatter dried coating is a blend of Methocel® E15LV and silica. The solidline contours represent constant peel strength in g/1.27 cm in a dryrelease test;

[0072]FIG. 6A is a cross-sectional view of a rubber roll before beingcured in a steam oven;

[0073]FIG. 6B is a schematic of the rubber rolls prepared in FIG. 6Abeing cured in an autoclave; and

[0074]FIG. 7 is a graphical representation of the force required toinitiate unnotched tear per unit thickness on samples of Dartek® T404coated on both sides with a coating of the invention comprisingMethocel® K35LV as a function of coat weight.

EXAMPLES

[0075] In the following examples a 0.001″ thick, monoaxially oriented,annealed at 150° C., polyamide66 film supplied by Enhance PackagingTechnologies Inc. of Whitby, Ontario under the trade name Dartek® T404was coated using a direct gravure coater supplied by Faustel Inc. ofGermantown, Wis. DuPont Dow Elastomers Inc. of Akron, Ohio supplied theuncured rubber compound used for dry and wet release testing, under thecommercial name of Viton®. The latter rubber compound contained 100parts of Viton® fluoroelastomer A201C, 3 parts of MgO, 6 parts ofCa(OH)₂ and 30 parts of carbon black.

[0076] In Examples 1 through 22, the coat weight of coated Dartek® T404release films was determined by washing off the coating with water fromthe 8″×8″ square sample. The weight loss in grams was multiplied by afactor of 14.9 to obtain the coat weight in lb/ream or in g/0.61 m². Thelatter technique was recommended by Morton International, Inc. PackagingAdhesives North America of Woodstock, Ill. in document #W-3020-641-02dated May 15, 1994.

Comparative Examples

[0077] Comparative examples 1 through 3 are aimed at evaluating therelease performance of Dartek® T404 coated with a conventional hightemperature, high humidity release coating. Release Coatings Inc. of NewYork supplied the high temperature, high humidity release coating underthe trade name of TM®-8836. This coating is conventionally used as atopical release coating on polyamide films and woven fabrics in therubber release industry, where the release film is subjected to hightemperature and high humidity conditions during the curing step.TM®-8836 contains 1-4% polytetrafluoroethylene (PTFE), 2-4% dipropyleneglycol methyl ether, less than 0.5% acetic acid and 4-6% NJ trade secret(NJTS Registry #00850201001-5360P) in 50-70% water. In total TM®-8836contains approximately 21% solids.

[0078] In order to illustrate the effect of varying coating compositionon the release performance of the coated films, TM®-8836 was dilutedwith water to three different dilution levels. The three differentcoating compositions along with their preparation method is outlinedbelow:

Comparative Example 1

[0079] 2.5 kg of TM®-8836 was added to 7.5 kg water to obtain 25%TM®-8836 concentrated solution in water. The solution was gently stirredfor 30-40 minutes.

Comparative Example 2

[0080] 3.5 kg water was added to 7.5 kg of the solution of ComparativeExample 1, to obtain 17% TM®8836 concentrated solution in water. Thesolution was gently stirred for 30-40 minutes.

Comparative Example 3

[0081] 7.11 kg water was added to 8 kg of the solution of ComparativeExample 2, to obtain 9% TM®8836 concentrated solution in water. Thesolution was gently stirred for 30-40 minutes.

[0082] Each of the solutions prepared in comparative examples 1 through3 were coated onto Dartek® T404 using a 165 quad cylinder on the directgravure coater from Faustel Inc. The conditions for each run aresummarized in Table 2. Each coating was laid on both sides of the filmin 2 separate passes and the coat weight was measured at the end of thesecond pass. The coat weights mentioned in Table 2 correspond to 2 sidecoated Dartek® T404. The coated films prepared in run no. 2, 4, 6 inTable 2 were subjected to dry and wet release testing, the details ofwhich are mentioned below. TABLE 2 COATING RUNS ON 25μ THICKDARTEKT ®404 ON FAUSTEL ® FOR COMPARATIVE EXAMPLES 1, 2 AND 3. ProcessEx. Line Coat Run (Coating Total speed Oven weight no. Substrate Used)No. solids % Fpm temp ° C. lb/ream/2 sides 1 25μ Dartek ®T404 1 5.25 10095 — first side 2 25μ Dartek ®T404 1 5.25 100 95 0.54 second side 3 25μDartek ®T404 2 3.57 150 100 — first side 4 25μ Dartek ®T404 2 3.57 150100 0.48 second side 5 25μ Dartek ®T404 3 1.89 150 100 — first side 625μ Dartek ®T404 3 1.89 150 100 0.32 second side

[0083] Release Testing Protocol

[0084] Two types of curing equipment are commonly used for curing rubberin the rubber release industry, viz. steam and gas ovens.

[0085] In a dry release test, approximately 2.5 g of rubber are pressedin between two release sheets at 5000 pounds (2.27 tons) in a 9 inch×9inch (22.86 cm×22.86 cm) press and 320° F. (160° C.) for 1 hr. The timerequired here is rubber dependent. For example, at least 35 minutes isrequired for Viton® rubber. Subsequently, the sample is cooled to roomtemperature and a strip (4″×½″) of the release sheet/rubber/releasesheet sandwich is cut and subjected to a 90 degree peel test at acrosshead speed of 10″/min using a peel tester. The peel test isconducted as per the Pressure Sensitive Tape Council's appendix B andASTMD1876. The above mentioned curing conditions for the latter releasetest were obtained after investigating the effect of temperature,pressure and cure time on the peel strength by means of experimentaldesign. The dry release test is designed on the assumption that humidityhas no effect on peel strength.

[0086] A wet release test is designed such that the high humidity curingcondition is taken into account. As per this test, a 4″×12″ sheet ofuncured Viton® rubber compound interleaved with the release film isrolled onto a stainless steel core, 6″ long having an outer diameter of¾″. A cross-sectional view of the rubber interleaved with the releasefilm mounted on the core is shown in FIG. 6(A). The latter roll isover-wrapped with a masking tape. This roll is fed into an autoclave forcuring at 160° C., 80 psi steam. The 1 L autoclave already contains 100ml water, which is separated from the rubber rolls using a wire mesh.This water turns to 80 psi steam at 160° C. A schematic of the autoclaveis shown in FIG. 6(B). The rubber roll is kept in the autoclave underlatter conditions for 35 minutes before cooling down the autoclave andtaking out the cured rubber rolls. Subsequently, the rubber rolls areunwrapped and the force required to peel off the release film from thecured rubber is determined as per the Pressure Sensitive Tape Council'sappendage B and ASTMD1876.

[0087] Release Test Results

[0088] Dry and wet release tests were conducted on TM®-8836 coatedDartek® T404 release films prepared in run no. 2, 4, 6 mentioned inTable 2 with uncured Viton® rubber compound. The results are mentionedin Table 3 and plotted as a function of coat weight in FIG. 1. It can beseen in FIG. 1 that the results of the dry release test are very closeto the results of the wet release test. This suggests that TM®-8836coating is relatively unaffected by moisture. Also, a minimum coatweight of 0.32 lb/ream of TM®-8836 is required per two sides of Dartek®T404 to achieve acceptable peel strength in dry and wet release tests.TABLE 3 DRY AND WET RELEASE TEST RESULTS OF RELEASE FILMS PREPARED INCOMPARATIVE EXAMPLES 1 TO 3 WITH VITON ® RUBBER. Dry release test resultWet release test result Av. Peel st., Av. Peel st., Ex. No. g/1.27 cm σg/1.27 cm σ 1 32.9 11 57 37 2 40.4 6.7 24.4 13.52 3 231.1 126.7 234.4145

[0089] The following examples are aimed at evaluating the dry and wetrelease strength of hydroxypropyl methylcellulose supplied by DowChemical Company under the trade name Methocel® coated on Dartek® T404.These examples illustrate the effect of different coat weights anddifferent grades of Methocel® on the release of Vitono rubber compoundfrom the surface of the coated film after rubber curing.

[0090] Eight different coating compositions (Examples 4 to 11) wereprepared to illustrate the effect of substitution and hydroxypropylmethylcellulose concentration in solution on coating performance. Thepreparation of each coating is described below and summarized in Table4. A description of the five different levels of substitution for theMethocel® products, of hydroxypropyl in hydroxypropyl methylcellulose ismentioned in Table 1. TABLE 4 COMPOSITION OF VARIOUS COATINGS PREPAREDFOR COATING DARTEK ®T404 FILM FOR EXAMPLES 4 TO 11. THE DASH LINE MEANS0%. Weight % Ex. Methocel ® Methocel ® Methocel ® Methocel ® No. K35LVE15LV A15LV J5MS Isopropanol Water 4 3.4 — — — 22.1 74.5 5 2.67 — — —17.35 79.98 6 1.53 — — — 9.94 88.53 7 0.7 — — — 4.55 94.75 8 0.2 — — —1.3 98.5 9 — 3.4 — — 22.1 74.5 10 — — 2 — 13 85 11 — — — 0.97 6.3 92.73

Example 4

[0091] 0.272 kg Methocel® K35LV was added to 1.768 kg isopropanol whilecontinuously stirring the solution to form a slurry. 5.96 kg cold tapwater was added to the latter slurry to make 8 kg of solution. Thesolution was continuously agitated for 30-40 minutes to form a clearviscous solution.

Example 5

[0092] 1.61 kg cold tap water was added to 5.875 kg of the solution ofExample 4 while gently stirring the solution. Stirring was continued for20-30 minutes.

Example 6

[0093] 3.99 kg cold tap water was added to 5.355 kg of the solution ofExample 5 while gently stirring the solution. Stirring was continued20-30 minutes.

Example 7

[0094] 8.97 kg cold tap water was added to 7.565 kg of the solution ofExample 6 while gently stirring the solution. Stirring was continued for20-30 minutes.

Example 8

[0095] 6.25 kg cold tap water was added to 2.5 kg of the solution ofExample 7 while gently stirring the solution. Stirring was continued for20-30 minutes.

Example 9

[0096] 0.272 kg Methocel® E15LV was added to 1.768 kg isopropanol whilecontinuously stirring the solution to form a slurry. 5.96 kg cold tapwater was added to the latter slurry to make 8 kg of solution. Thesolution was continuously agitated for about an hour to form a clearviscous solution.

Example 10

[0097] 0.16 kg Methoce® A15LV was added to 1.04 kg isopropanol to formslurry. To this was added 6.8 kg cold tap water while gently stirringthe solution. Stirring was continued for about an hour until a clearsolution was obtained.

Example 11

[0098] 0.16 kg Methocel® J5MS was added to 1.04 kg isopropanol whilecontinuously stirring the solution to form slurry, having pH less than7.5. To this was added 15.3 kg cold tap water with trace amounts ofNH₄OH to adjust the pH above 8.5. The solution was continuously agitatedfor 30-40 minutes to form a clear viscous solution.

[0099] Coating Runs

[0100] The above mentioned coatings of Examples 4 to 10 were coated ontoDartek® T404 using 165 quad cylinder on the direct gravure coater fromFaustel Inc. The coating prepared in Example 11 was coated onto Dartek®T404 using a number 90 tri-helical cylinder. The values of coatingparameters viz. line speed and temperature of the oven is set out inTable 5. The first side is coated in the first run and then the uncoatedside is coated in the second run e.g. 25μ thick Dartek® T404 is coatedwith the coating produced in Example no. 4, in run no. 7 and thensubsequently, the uncoated side of the film is coated in run no. 8.TABLE 5 Coatings applied to Dartek T404 film on Faustel. Coat Total LineOven weight Run. Ex. solids speed temp lb/ream/ No. Substrate No. % fpm° C. 2 sides 7 25μ Dartek ®T404 4 3.4 150 104 — first side 8 25μDartek ®T404 4 3.4 150 104 0.2533 second side 9 25μ Dartek ®T404 5 2.67150 104 — first side 10 25μ Dartek ®T404 5 2.67 150 104 0.3725 secondside 11 25μ Dartek ®T404 6 1.53 150 100 — first side 12 25μ Dartek ®T4046 1.53 150 100 0.2235 second side 13 25μ Dartek ®T404 7 0.7 150 100 —first side 14 25μ Dartek ®T404 7 0.7 150 100 0.1788 second side 15 25μDartek ®T404 8 0.2 150 102 — first side 16 25μ Dartek ®T404 8 0.2 150102 0.149 second side 17 25μ Dartek ®T404 9 3.4 150 102 — first side 1825μ Dartek ®T404 9 3.4 150 102 0.3874 second side 19 25μ Dartek ®T404 102 150 105 — first side 20 25μ Dartek ®T404 10 2 150 105 0.3278 secondside 21 25μ Dartek ®T404 11 0.97 100 110 — first side 22 25μDartek ®T404 11 0.97 100 110 0.64 second side

[0101] Release Test Results

[0102] The two-side hydroxypropyl methylcellulose coated Dartek® T404release films prepared in run nos. 8, 10, 12, 14, 16, 18, 20, 22 inTable 5 were subjected to wet and dry release tests with uncured Viton®rubber compound. The peel strengths obtained in both dry and wet releasetests along with their standard deviations for the Dartek® T404 filmscoated on both sides with the coatings listed in Table 4 are mentionedin Table 6 and Table 7, respectively which appear hereafter. The resultsin Table 6 and 7 clearly show that higher coat weights of hydroxypropylmethylcellulose are required for acceptable release (less than 200g/1.27 cm) in a dry release test than in a wet release test. UncoatedDartek® T404, sticks to Viton® in both wet and dry release tests. Thefilm breaks at about 2000 g/1.27 cm during the peel test in the lattercase. Therefore at zero coat weight the peel strength is equal to 2000g/1.27 cm. FIG. 1 compares the performance of hydroxypropylmethylcellulose (i.e. Methocel® K35LV coated Dartek® T404 produced inrun nos. 8, 10, 12, 14, 16 in Table 5) with the release test results ofTM®-8836 coated Dartek® T404 from Comparative Examples 1 to 3. Allpoints below the horizontal line at 200 g/1.27 cm in FIG. 1 satisfy therelease criteria.

[0103] The dry release test results shown as open symbols in FIG. 1clearly show that the coat weight required for adequate release in caseof Methocel® K35LV is half of what is needed with TM®-8836.

[0104] According to FIG, 1, Methocel® K35LV coated Dartek® T404 providesadequate release (less than 200 g/1.27 cm) at coating weights as low as0.15 lb/ream in a wet release test. The latter coat weight includes twosided coated Dartek® T404 film. Since release is checked from Viton®rubber on each side of the coated film, it can be said in a more generalsense that 0.075 lb/ream of Methocel® K35LV on a polyamide 66 filmsurface gives peel strengths well within the acceptable criteria (below200 g/1.27 cm) in a wet release test. It is impractical to controlcoating weights of less than 0.075 lb/ream per side with the existingcoating technology and difficult to measure them. The coat weight istraditionally measured by washing away the coating on a square sample ofthe coated film to obtain the change in weight. This change in weight isthen multiplied by an appropriate factor assuming uniform coating togive the coat weight in lb/ream.

[0105] The wet release data for Methocel® K35LV shown in FIG. 1 ismodeled using a 3 parameter exponential decay equation of the followingform:

y=y ₀ +a.e ^(−bx)  (1)

[0106] where, y is the peel strength in g/1.27 cm and x is the two sidedcoat weight in lb/ream.

[0107] A good fit to the wet release test data of Methocel® K35LV coatedDartek® T404 film is obtained using Equation (1), with y₀ equal to 22.65g/1.27 cm (g/1.27 cm); and a and b equal to 1977 g/1.27 cm (g/1.27 cm)and 290 ream/lb(0.61 m²/gm.) respectively. According to Equation (1),the two sided coat weights required for acceptable release, i.e. 200g/1.27 cm, in a wet release test is equal to 0.008 lb/ream. This meansthat only 0.004 lb/ream of Methocel® K35LV is required per side foradequate release in a wet release test. Based on the above interpolationusing Equation (1), a minimum of 0.004 lb/ream of hydroxypropylmethylcellulose containing molar hydroxypropyl substitution of 0.21,coated on a polyamide66 film provides release in high temperature andhigh humidity conditions. According to Equation (1), the minimum 2 sidecoat weight depends on the release criteria e.g. release criteria of 800g/1.27 cm would require 0.003 lb/ream of Methocel® K35LV.

[0108] Different grades of hydroxypropyl methylcellulose can be obtainedby changing the molar hydroxypropylyl substitution as mentioned inTable 1. FIG. 2 shows the constant peel strength contours for differentgrades of hydroxypropyl methylcellulose at varying coat weights resultsshown on Table 6 and 7) in wet and dry release tests. It can be seenthat all grades of hydroxypropyl methylcellulose give adequate releasein both wet and dry release tests at a minimum coat weight of 0.15-0.5lb/ream coated equally on both sides of the polymer film or 0.075-0.25lb/ream per side. The preferred grades of hydroxypropyl methylcellulosefor the release coating on polymer film are those containing 0-0.60molar hydroxypropyl substitution. TABLE 6 DRY RELEASE TEST RESULTS WITHVITON ® RUBBER AV. PEEL ST., Ex. No. G/1.27 CM σ 4 56.3 18.2 5 40.5 7.46 64.3 30.4 7 137.7 45.7 8 254.1 20.3 9 76.5 68.7 10 42.6 7.1 11 113.4092.96

[0109] TABLE 7 WET RELEASE TEST RESULTS WITH VITON ® RUBBER Av. Peelst., Ex. No. g/1.27 cm σ Observations 5 36.50 16.50 No fibrillation,significant transfer (gummy), clear 6 18.00 8.00 No fibrillation at all,significant transfer (gummy), clear 7 26.33 7.11 Slight fibrillation, notransfer, clear 8 9.75 2.63 Insignificant transfer, lesser fibrillation9 18.75 8.69 No fibrillation, no transfer 10 45.78 12.15 Slighttransfer, no fibrillation 11 87.56 59.06 No fibrillation, very gummy

[0110] Haze Test

[0111] After a wet release test, the haze of all the films tested forwet release in Table 7 was measured as per ASTMD1003. To generate acontrol sample, an uncoated Dartek® T404 sample was kept at 160° C., 80psi steam for 35mins in an autoclave without any contact with the rubbercompound. The latter uncoated sample was also subjected to haze test asper ASTMD1003. The result of the haze test are mentioned in Table 8.FIG. 3 shows contours of constant % haze for Dartek® T404 film coatedwith different grades of hydroxypropyl methylcellulose on both sides atvariable coat weights. As listed in Table 8, the haze of Dartek® T404 is1.6%. It can be clearly seen in FIG. 3, that the hydroxypropylmethylcellulose grade having 0.12-0.32 molar hydroxypropyl substitutionhas lower haze than uncoated Darteke® T404 film. TABLE 8 HAZE TESTRESULTS AFTER A WET RELEASE TEST WITH VITON ® RUBBER Ex. No. Haze, %DARTEK ® T404 (control) 1.60 5 1.40 6 1.70 7 1.10 8 1.90 9 1.60 10  2.3011  2.40

[0112] Grave's Tear Test

[0113] The hydroxypropyl methylcellulose coated Dartek® T404 filmslisted in Table 7 were also tested for unnotched tear strength afterthey were subject to wet release testing. The idea was to investigatethe effect of hydroxypropyl methylcellulose on the force required toinitiate tear of polyamide66 film after the films were exposed to hotand humid conditions. The Grave's test was performed as perASTMD1004-94a. The results of Grave's tear test are mentioned below inTable 9. TABLE 9 GRAVE'S UNNOTCHED TEAR TEST RESULTS AFTER EXPOSING THESAMPLES TO 60° C., 80 PSI FOR 35 MINS. Grave's tear results (MD) Grave'stear results (TD) Load/thck@auto Load/thck@auto Ex. No. brk, lbf/in σbrk, lbf/in σ DARTEK 212.76 59.24 718.82 50.52 T404NA 5 260.40 152.72742.89 68.57 6 253.39 64.90 625.27 114.00 7 254.97 128.75 731.15 131.648 943.24 44.33 673.15 140.01 9 263.08 115.23 744.22 132.30 10  914.8681.56 932.25 118.49 11  808.23 717.73 885.89 220.89

[0114] The force required to initiate un-notched tear per unit thicknesson Methocel® K35LV coated Dartek® T404 samples as a function of coatweight is shown in FIG. 7. It can be seen that as little as 0.18 lb/reamof Methocel® K35LV per two sides, increases the tear strength/thicknessof the release film by approx. 22% in the machine direction. However, nosuch benefit is seen in the transverse direction. FIG. 7 suggests thatthe tear strength per thickness is independent of Methocel® K35LVcoating in transverse direction for the coat weights investigated.Similar results were obtained for all other grades of hydroxypropylmethylcellulose (molar hydroxypropyl substitution from 0-0.82) coatedDartek® T404.

[0115] Wettability 0f Dartek® T404

[0116] The tension of TM®-8836 is 25.88-35.02 dyn/cm as mentioned in theproduct literature supplied by Release Coatings Inc. of New York. Butthe surface tension of the Dartek® T404 film coated with the latter is48.54 dyn/cm as determined by contact angle measurements andapproximated by harmonic mean method as per ASTMD5946-99. The surfacetension of Dartek® T404 is in-between 45-50 dyn/cm. This suggests thatTM®-8836 does not wet out the Dartek® T404 film completely. The lattersuggestion was confirmed by looking at the surface of TM®-8836 coatedDartek® T404 film under the microscope. Green colored aggregates ofTM®-8836 were observed on the surface. On the other hand nothing wasseen on the hydroxypropyl methylcellulose coated Dartek® T404. But adrop of water on the latter emitted blue color as observed under themicroscope. Later on it was observed that hydroxypropyl methylcellulosemolecules even in the absence of polyamide66 molecules emitted bluecolor when wetted with water. This suggest that hydroxypropylmethylcellulose forms a continuous layer on polyamide66 film.

[0117] The following examples were aimed at evaluating the effect ofadding silica to hydroxypropyl methylcellulose solution in water onprocessability and release from cured rubber in dry and wet releasetests. A high film-forming grade of hydroxypropyl methyl cellulosecontaining 0.23 hydroxypropyl molar substitution was supplied by DowChemical Company under the commercial name of Methocel® E15LV. Silicawas obtained in colloidal form for ease of mixing. The colloidal silicaused for these examples was supplied by E.I. Du Pont de Nemours andCompany, under the commercial name of Ludox® CL-P. Ludox® CL-P is apositively charged sol made by coating negative silica particles with apositive layer of alumina. The size of the latter particles is around 22nm with a specific surface area of 140 m²/g. Ludox® CL-P contains 40 wt% silica and has a pH in-between 3.5-4.5. In order to illustrate theeffect of Ludox® CL-P content in the coating composition onprocessability and release characteristics, five different coatings wereprepared. The compositions of these five coatings are summarized inTable 10 and their preparation method is discussed below. TABLE 10COMPOSITIONS FOR COATINGS. Weight % Example Methocel ® No. E15LV Ludox ®CL-P Isopropanol Water 12 3 1 13 83 13 2.44 0.81 10.57 86.18 14 1.870.62 8.1 89.40 15 1.06 1.18 4.6 93.14 16 0.48 0.54 2.09 96.89

Example 12

[0118] 0.3 kg Methocel® E15LV was added to 1.3 kg isopropanol whilecontinuously stirring the solution to form slurry. 8.3 kg cold tap waterwas added and followed by 0.1 kg Ludox® CL-P to the latter slurry toobtain 10 kg of coating solution. The solution was continuously agitatedfor about 30 minutes to form a clear viscous solution.

Example 13

[0119] 1.65 kg cold tap water was added to 7.175 kg of the coatingsolution of Example 12. The mixture was gently stirred for 20 minutes.

Example 14

[0120] 2.1 kg cold tap water was added to 6.885 kg of the coatingsolution of Example 13. The mixture was gently stirred for 20 minutes.

Example 15

[0121] 5.6 cold tap water was added to 7.535 kg of the coating solutionof Example 14, followed by 0.11 kg Ludox® CL-P. The mixture was gentlystirred for 20 minutes.

Example 16

[0122] 4.8 kg cold tap water was added to 4 kg of the coating solutionof Example 15. The mixture was gently stirred for 20 minutes.

[0123] The above prepared coatings of Examples 12 through 16 were coatedon Dartek® T404 using 165 quad cylinder on a direct gravure coater fromFaustel Inc. The values of coating parameters corresponding to each runare mentioned in Table 11. TABLE 11 COATINGS ON DARTEK ®T404 ON FAUSTELTOTAL RUN EX. SOLIDS LINE COAT WEIGHT NO. SUBSTRATE NO. % SPEED FPM OVENTEMP° C. LB/REAM/2SIDES 23 25μ 12 3.4 150 101 — Dartek ®T404 first side24 25μ 12 3.4 150 101 0.75 Dartek ®T404 second side 25 25μ 13 2.75 150100 — Dartek ®T404 first side 26 25μ 13 2.75 150 100 0.51 Dartek ®T404second side 27 25μ 14 2.1 200 100 — Dartek ®T404 first side 28 25μ 142.1 200 100 0.33 Dartek ®T404 second side 29 25μ 15 1.53 200 100 —Dartek ®T404 first side 30 25μ 15 1.53 200 100 0.31 Dartek ®T404 secondside 31 25μ 16 0.7 200 100 — Dartek ®T404 first side 32 25μ 16 0.7 20090 0.24 Dartek ®T404 second side

[0124] It was observed that small amounts of Ludox® CL-P in aqueousMethocel® E15LV solution resulted in higher transfer of coating athigher percent solids in the solution. FIG. 4 shows the increase in coatweight with increase in percent solids in the solution for variouscoatings investigated in Examples 1 to 16. The coat weight correspondingto the coatings containing TM®-8836, Methocel® K35LV and Methocel® E15LVlevel off or dorp at approximately 3% solids. This is expected as theviscosity of the solution increases with increasing % solids, whichmakes it increasingly difficult for the cylinders to transfer thecoating onto the film. On the other hand a solution containing Methocel®E15LV/Ludox® CL-P ratio equal to 3/1, where Methocel® E15LV accounts for1.86% to 3% of the solution, gives surprisingly higher transfer of thecoating to Dartek® T404 above 3% solids. Ludox® CL-P is an aqueouscolloidal dispersion of very small silica particles. The silica used inLudox® CL-P is made up of negative silica particles with a positivelayer of alumina. It is speculated that the positive charge imparted tothe coatings of Examples 12 through 16, because of Ludox® CL-P helps thetransfer of the release coating on to the Dartek® T404 film which hasamide negative ions on the surface. This property is in addition to theusual behaviour of silica and other particulate solids which act asprocessing aids for the film to be coated.

[0125] Release Testing

[0126] The results of wet and dry release tests performed on Dartek®T404 film samples coated with a blend of hydroxypropyl methylcelluloseand Ludox® CL-P corresponding to Run Nos. 24, 26, 28, 30, 32 in Table 11with uncured Viton® rubber compound, are mentioned in Table 12. Inaddition to the coated films mentioned in Table 12, a sample of Dartek®T404 film hand-wiped with Ludox® CL-P, so as to achieve a coat weight of0.8 lb/ream per two sides was also subjected to dry release testing withuncured Viton® rubber compound. The latter sample stuck to the curedrubber. FIG. 5 shows the effect of increasing the weight fraction ofsilica in the dried coating on a two side coated Dartek® T404 film. Itcan be clearly seen that for a particular coat weight of a two sidecoated Dartek® T404 film, 0.01-0.60 weight fraction of silica in thedried coating reduces the peel strength. The minimum in peel strength isfound around 0.15 silica wt fraction. However, excess amount of silica(above 0.60) on the surface increases the peel strength with completeadhesion (peel strength of 2000 g/1.27 cm) at 100% silica in the driedcoating. TABLE 12 Dry and Wet release test results of release filmsprepared with Viton ® rubber. The dash line means that results are notavailable. Dry release test result Wet release test result Av. Peel st.,Av. Peel st., Ex. No. g/1.27 cm σ g/1.27 cm σ 12 32.8 5.1 36.33 12.67 1364.7 45.2 — — 14 52.2 23.1 — — 15 62.3 31.7 — — 16 138.4 24.2 51.2528.4 

[0127] The following Examples 17 through 18, show that the mixture ofhydroxypropyl methylcellulose and silica, when coated onto the surfaceof various polymer films impart high temperature and high humidityrelease characteristics to the film. In this example, three differentfilms, which have a melting point above 160° C. (temperature of wet anddry release test) were coated with a mixture of hydroxypropylmethylcellulose and silica. The films used, included 25 microns thickbiaxially oriented polyester supplied by E. I. DuPont de Nemours underthe trade name of Mylar®, 100 microns thick heat stabilized cast Nylon66film supplied by Enhance Packaging Technologies Inc. under the tradename of Dartek® C917 and 25 microns thick biaxially oriented Nylon6 filmsupplied by Pt. Kolon Ina, Indonesia under the trade name of Amidroll®.Once coated, the latter films were subject to wet and dry releasetesting. The hydroxypropyl methylcellulose was supplied by Dow ChemicalCompany under the trade name Methocel®. The colloidal silica used in thecoating formulation was supplied by W R Grace under the trade name ofLudox® CL-P (formerly owned by E. I. du Pont de Nemours and Company).TABLE 13 Compositions for coatings. Weight % Example Methocel ® No.K35LV Ludox ® CL-P Isopropanol Water 17 2.67 0 17.33 80.0 18 3.35 1.1221.80 73.73

Example 17

[0128] 0.267 kg Methocel® K35LV was added to 1.733 kg isopropanol whilecontinuously stirring the solution to form a slurry. 8.0 kg cold tapwater was added to the latter slurry and the resulting solution wassubject to high shear agitation for 30-40 minutes to form a clearbrownish viscous solution. Thus 10 kg coating solution was prepared.

Example 18

[0129] 0.335 kg Methocel® K35LV was added to 2.18 kg isopropanol whilecontinuously stirring the solution to form a slurry. 7.373 kg cold tapwater was added to the latter slurry and the resulting solution wassubject to high shear agitation for 30-40 minutes to form a clearbrownish viscous solution. Finally 0.112 kg Ludox® CL-P was added to thesolution and the agitation was continued for another 20-30 minutes. Thus10 kg coating solution was prepared.

[0130] The above prepared coatings of Examples 17 through 18 were coatedon various polymer films using 165 quad cylinder on a direct gravurecoater from faustel Inc. The values of coating parameters correspondingto each run are mentioned in Table 14. TABLE 14 Coatings on variouspolymer films on Faustel Total % SILICA Run Ex. solids Line speed OvenCoat weight IN DRIED No. Substrate No. % fpm temp ° C. lb/ream/2 sidesCOATING 33 25μ Mylar ® 17 2.67 200 90 0 first side 34 25μ Mylar ® 172.67 200 90 0.16 0 second side 35 100μ 18 3.8 200 60 — Dartek ®C91 7first side 36 100μ 18 3.8 200 0.31 12 Dartek ®C91 7 second side 37 25μ18 3.8 200 55 Amidroll ® first side 38 25μ 18 3.8 200 55 0.27 12Amidroll ® second side

[0131] The results of wet and dry release tests performed on variouspolymer films coated with a blend of hydroxypropyl methylcellulose andLudox® CL-P corresponding to run nos. 34, 36, 38 in Table 14 withuncured Viton® rubber compound is mentioned in Table 15. The value ofpeel strength for uncoated samples of the films coated in Table 14 arealso mentioned in Table 15. TABLE 15 Dry and Wet release test results ofrelease films prepared in Table 14 With Viton ® rubber. The dash linemeans that results are not available. Coat- ing Dry release Wet releaseFrom test result test result Ex- Av. Av. Run. Film ample Peel st., Peelst., Nos. Substrate. No. g/1.27 cm σ g/1.27 cm σ — 25μ None Stuck —stuck — Mylar ® 34 25μ 17 189 63 10  5 Mylar ® — 100μ None stuck — Stuck— Dartek ®C9 17 36 100μ 18 32.25 6.06 74 30 Dartek ®C9 17 — 25μ NoneStuck — film melts and is no Amidroll ® longer there 38 25μ 18 6.4 1.68film melts and is no Amidroll ® longer there

[0132] The following Example 19 is to establish the maximum limit of theamount of hydroxypropyl methylcellulose in the coating solution. Traceamount of silica is also added to the latter solution for ease ofprocessability in the coater. The latter solution can be used with asuitable cylinder to obtain the desired coat weight on the polymerfilms. The low viscosity grade of hydroxypropyl methylcellulose wassupplied by Dow Chemical Co. under the trade name of Methocel® K3premium LV. TABLE 16 Composition for coating Weight % Example Methocel ®K3 No. premium LV Ludox ® CL-P Isopropanol Water 19 15.0 5.1 30 49.9

[0133] The formulation for the coating solution is mentioned in Table16. In order to prepare 7 kg of coating solution, 1.05 kg Methocel® K3premium LV was slowly added to 2.1 kg of isopropanol while continuouslyagitating the mixture. The mixture was agitated for 30 minutes to makesure that Methocel® K3 premium LV powder was fully dispersed inisopropanol and no lumps were formed. Subsequently, 3.49 kg cold tapwater (5° C.-25° C.) was added while stepping up the agitation. Theresulting mixture was agitated at high speed for 1-2 hours till a clearbrownish viscous solution was formed. Finally, 357 g of Ludox® CL-P wasadded and the solution was agitated for another 30 minutes. The coatingsolution had 17% solids content.

[0134] The thus prepared solution was coated onto 25 microns thickmonoaxially oriented Nylon66 film supplied by Enhance PackagingTechnologies Inc. under the trade name of Dartek® T404. The coating runwas conducted on the direct gravure coater from Faustel at 200 ft/minusing a 180 quad cylinder. The exit film temperature was 88° C. and thecoat weight achieved after coating the film in two separate passes wasabout 0.84 lb/ream per both sides. The coated film was subject to dryand wet release test with Viton® rubber compound. A force of 12±7 g/1.27cm was required to strip off the coated film from cured Viton® rubber ina dry release test and a force of 10±5 g/1.27 cm was required in a wetrelease test.

[0135] The following Example 20 is to illustrate that a mixture ofhydroxypropyl methylcellulose having different levels of hydroxypropylmolar substitutions in the coating solution when coated onto a polymerfilm gives adequate release performance both in dry and wet releasetests. A trace amount of silica is also added to the latter solution forease of processability in the coater. The various grades ofhydroxypropyl methylcellulose having different levels of hydroxypropylsubstitution were supplied by Dow Chemical Co. under the trade name ofMethocel® (see Table 1).

Example 20

[0136] TABLE 17 Composition for coating Weight % Example Methocel ® K35Methocel ® E15 Methocel ® A15 No. LV premium LV LV Ludox ® CL-P Water 200.91 2.37 1.13 1.49 94.1

[0137] The formulation for the coating solution is mentioned in Table17. In order to prepare 15 kg of coating solution, 136.5 g of Methocel®K35LV, 355.5 g of Methocel® E15 premium LV and 169.5 g of Methocel®A15LV were collected in a container. The latter mixture (661.5 g intotal) of various grades of Methocel® powder was added to 14.12 kg ofcold tap water while continuously agitating the mixture at high speed.The mixture was agitated for 1-2 hours to make sure that a clear viscoussolution was obtained. 223.5 g of Ludox® CL-P was added and the solutionwas agitated for another 30 minutes. The coating solution had 5% solidscontent.

[0138] The thus prepared solution was coated onto 25 microns thickmonoaxially oriented Nylon66 film supplied by Enhance PackagingTechnologies Inc. under the trade name of Dartek® T404. The coating runwas conducted on the direct gravure coater from Faustel at 250 ft/minusing a 180 quad cylinder. The exit film temperature was 70° C. and thecoat weight achieved after coating the film in two separate passes wasabout 0.54 lb/ream per both sides. The coated film was subject to dryand wet release test with Viton® rubber compound. A peel strength of8.83±4.11 g/1.27 cm was required to strip off the coated film from curedViton® rubber in a dry release test and a force of 13.2±11.4 g/1.27 cmwas required in a wet release test.

[0139] The following Example 21 shows the effect of coating variousfilms with hydroxypropyl methylcellulose containing solutions on theirrelease performance in a dry curing release test with carbon fiberreinforced expoxy resin. The 292μ thick carbon fiber reinforced epoxysheets used in this example, were supplied by Fujikura CompositeAmerica, Inc, California. The latter composite sheet is used by FujikuraComposites for making golf shafts.

Example 21

[0140] The five films selected for the dry release test with carbonfiber reinforced epoxy resin are:

[0141] SAMPLE 1. Uncoated, monoaxially oriented 25μ thick Nylon66 filmobtained from Enhance Packaging Technologies under the trade name ofDartek® T404.

[0142] SAMPLE 2. Uncoated biaxially oriented, 25μ thick Nylon6 filmobtained from Pt. Kolon Ina, Indonesia under the trade name ofAmidroll®.

[0143] SAMPLE 3. Dartek® T404 coated in Run 15 and 16 with Methocel®K35LV containing solution prepared in Example 8.

[0144] SAMPLE 4. Amidroll® coated in Run 37 and 38 with a mixture ofMethocel® K35LV and Ludox® CL-P containing solution prepared in Example18.

[0145] SAMPLE 5. Dartek® T404 coated in Example 19 with a mixture ofMethocel® K3LV and Ludox® CL-P containing solution.

[0146] Description of the Dry Release Test with Fiber Reinforced Plastic

[0147] In a dry release test for Fiber Reinforced Plastic, an uncuredcomposite sheet comprising of a mixture of fiber and resin in a sheetform on a paper or polymer film carrier is used. Approximately 1.2 g (6cm×6 cm square sample) of the latter composite sheet is pressed inbetween two release sheets at 5000 pounds (2.27 tons) in a 9 inch×9 inch(22.86 cm ×22.86 cm) press and 325° F. (163° C.) for 1.5 hr.Subsequently, the sample is cooled to room temperature and a strip(4″×½″) of the release sheet/cured composite sheet/release sheetsandwich is cut and subjected to a 180 degree peel test at a crossheadspeed of 10″/min using a peel tester. The peel test is conducted as perthe Pressure Sensitive Tape Council's appendix B and ASTMD1876. The dryrelease test is designed on the assumption that humidity has no effecton peel strength. The peel test is conducted in-between the film and theface of the composite sheet comprising of cured resin and fibers.

[0148] Samples 1 through 5 were subject to dry release test forcomposites. The results are as follows: TABLE 18 Dry release testresults of release films With Carbon Fiber Reinforced Epoxy CompositeSheets The dash line means that results are not available. Dry releasetest result Sample. No. Av. Peel st., g/1.27 cm σ 1 282  115  2 stucklike glue — 3 5 2 4 5 2 5 7 2

[0149] It can be clearly seen in the release test results mentioned inTable 18, that coating Nylon66 or Nylon6 films with hydroxypropylmethylcellulose or a mixture of hydroxypropyl methylcelllose and silicaenhances its release from the cured epoxy composite sheet.

[0150] The following example is to establish the maximum limit ofhydroxypropyl methylcellulose concentration in water which can bediluted further with water and (or) any organic solvent like isopropylalcohol.

Example 22

[0151] TABLE 19 Formulation: I II Methocel K3LV, % 40.06 5.79 IPA, %0.00 11.11 Water, % 59.94 83.10 Total solids, % 40.10 5.79

[0152] A dense solution of hydroxypropyl methylcellulose in water wasmade as per Formulation I in Table 19. In order to make 6.34 kg oflatter solution, 3.8 kg hot water (90-100° C.) was added to 2.54 kgMethocel® K3 Premium LV and subsequently the mixture was subjected tohigh shear for approximately 2 hrs. The dense solution was left at roomtemperature for 24 hrs to cool down. The advantage of this densesolution is that it can be readily diluted with solvents to whatever %solids are required by the employed coating process. Making concentratedsolution of hydroxypropyl methylcellulose in water makes the storage andtransportation of the coating more cost effective.

[0153] For a direct gravure coating application with a 180 quadcylinder, the above prepared, dense solution was diluted to FormulationII shown in Table 19. The dilution was performed by adding 2 kgisopropyl alcohol to 2.6 kg of slurry prepared as per Formulation IVunder high shear agitation. After agitating for approximately 30 minutes13.4 kg of cold tap water was added. The solution was agitated until aclear brownish viscous solution was obtained. In this way 18 kg ofcoating solution as per Formulation II in Table 19 was obtained.

[0154] The thus prepared solution was coated onto 25 microns thickmonoaxially oriented Nylon66 film supplied by Enhance PackagingTechnologies Inc. under the trade name of Dartek® T404. The coating runwas conducted on the direct gravure coater from Faustel at 250 ft/minusing a 180 quad cylinder. The exit film temperature was 45° C. and thecoat weight achieved after coating the film in two separate passes wasabout 0.54 lb/ream per both sides. The coated film was subject to dryrelease test with Viton® rubber compound. A peel strength of 13.25±0.88g/1.27 cm was required to strip off the coated film from cured Viton®rubber in a dry release test.

[0155] Hydroxypropyl methylcellulose with different levels ofhydroxypropyl molar substituion can be coated onto the polymer filmusing a variety of coating processes. These coating processes depend ona number of parameters including rheological and surface properties ofthe coating solution. More information on these parameters can be foundin Edgar B. Gutoff, Edward D. Cohen, “Coating and DryingDefects-Troubleshooting Operating Problems”, John Wiley & Sons Inc., NY(1995).

[0156] In general rotogravure coating can handle coating solutionshaving viscosity of up to approximately 1000 cps with proper selectionof the coating cylinder. More viscous coatings can be handled in othercoating processes like extrusion coating and slot die coating. Theviscosity of coating solution increases with increasing content ofHydroxypropyl methylcellulose in the solution (See Dow Chemical Company,“Methocel Cellulose Ethers Technical Handbook” published June 1997).

[0157] Although hydroxypropyl methylcellulose is infinitely soluble incold water, the practical limit for incorporation of hydroxypropylmethylcellulose in water is about 40%. Increasing the hydroxypropylmethylcellulose content in the solution above 40% gives rise toproblems, such as incomplete wetting.

[0158] Usually the coating solution is made at higher percent solids inorder to eliminate handling and storage problems. Depending on themixing facilities available 15-40% of hydroxypropyl methylcellulose ismixed with water or a mixture of organic solvents and water. Tracequantity of colloidal silica may also be mixed into the latter solutionfor ease of processability. Some typical formulations can be found inExamples 1-22. This concentrated solution is then diluted so that theviscosity and percent solids in the coating are suitable for the coatingprocess employed. Depending on the level of hydroxypropyl molarsubstituion in the Hydroxypropyl methylcellulose used in theconcentrated solution, it can be diluted to 0.2%-17% solids.

[0159] The following example is to show the best mode for making arelease film by coating Dartek® T404 (supplied by Enhance PackagingTechnologies, Whitby) with a mixture of Methocel® K3LV premium from DowChemical Co., and Ludox®CI-P from W R Grace & Co. A 60 inch wide tworoll coater equipped with a turning bar was used to coat Dartek® T404 onboth sides in a single pass.

Example 23

[0160] First a coating mixture concentrate containing 17% solids wasprepared. The ingredients of the coating mixture concentrate along withtheir weight percent compositions and sequence of addition are set outin Table 20.

[0161] A stepwise description for preparing one 300 kg batch of aconcentrate of coating solution TABLE 20 The components with theirrespective weight percent in the blended solution. Weight in kg forSequence. % wt. in coating making 300 kg No. Ingredient solutionsolution 1 Isopropyl alcohol 30.0 90.0 2 Methocel ® K3LV 15.0 45.0premium grade 3 Cold tap Water 49.9 149.7 4 Ludox ® Cl-P  5.1 15.3 Total17.0% solids 300

[0162] follows:

[0163] Requirements: A high shear mixer, a mixing tank capable ofstoring 350 kg of water, Supply of clean cold tap water at 5° C.-25° C.,calibrated weighing scale measuring up to at least 1 decimal places, two45 gallon plastic drums; and the mixture should be prepared at roomtemperature.

[0164] 1. 90.0 kg of isopropyl alcohol was poured into the empty mixingtank.

[0165] 2. 45 kg Methocel® K3LV premium grade powder was slowly added tothe mixing tank and the mixture was subjected to high shear in order toprepare a slurry.

[0166] 3. The mixture was agitated until the particles of Methocel® K3LVpremium grade were evenly dispersed (up to 10-15 minutes). Care wastaken to ensure that no Methocel® K3LV premium grade lumps were formed.

[0167] 4. The Methocel® K3LV premium grade slurry was agitated inisopropyl alcohol while 149.7 kg of cold tap water was slowly added tothe slurry.

[0168] 5. The mixture was agitated until a clear viscous solution withno lumps was obtained. The agitation was continued for at least 30minutes.

[0169] 6. 15.3 kg Ludox® CI-P was added to the mixture whilecontinuously agitating the mixture.

[0170] The 300 kg of blended solution prepared above were stored in 2plastic 45 gallon drums. The lid of the container was tightly closed.The filled drums were stored at room temperature. The viscosity of theblended solution as measured by Brookfield viscometer was approximately750 cp at 25° C. This concentrate of coating solution (17% solids) wasdiluted to managable solids content (4.5% solids) for the coating.

[0171] A stepwise description of preparing a 150 kg batch of coatingsolution containing 4.5% solids follows:

[0172] Requirements: 1 clean 45 gallon drum, a clean agitator, supply ofclean cold tap water at 5° C.-25° C., calibrated weighing scalemeasuring up to at least 1 kg; and the mixture should be prepared atroom temperature

[0173] 1. 40.0 kg of 17% solids coating solution concentrate was placedin a clean 45 gallon drum.

[0174] 2. The solution was agitated in the drum while adding 95 kg coldtap water followed by 15.0 kg isopropanol.

[0175] 3. The resulting 150 kg solution was agitated mildly for at least15 minutes before it was used.

[0176] 4. One batch (150 kg) of the coating solution (4.5% solids) coatsapproximately 305 kg of 25 microns thick Dartek® T404 (60 inches wide)at a coat weight of 0.4 lb./ream per both sides.

[0177] If the above-prepared solution is used at a later date then thelid of the container containing the coating solution is tightly closedand the container is stored at room temperature.

[0178] Coating Run

[0179] The film was coated on both sides in a single pass using theturning bar. The coating solution was agitated for at least 15 minutesprior to use.

[0180] Tension requirements were worked out by considering that theoptimum tension required for coating 25 micron thick Dartek® T404 isabout 703.5 psi (38 lbs for 54 inches wide 1 mil thick Dartek® T404),which corresponds to a strain of about 0.48% in the oven.

[0181] The exit temperature of the film was at least 60° C.

[0182] The coating conditions for each pass were as follows: Line speed,ft/min: 575 (175 m/min) EDT Prim.: 3 KW

[0183] Coated Film Temperature: minimum=60° C., maximum=70° C. Dry bondrolls: off Chill roll: As required to achieve room temperature wind Coatweight: 0.20 ± 0.05 lb./ream per side

[0184] The coat weight of the film was measured every mill roll. Thecoat weight was determined as per the procedure mentioned in Document#W-3020-641-02.

[0185] The coated film was subject to dry and wet release test withViton® rubber compound. A force of 40±15 g/1.27 cm was required to stripoff the coated film from cured Viton® rubber in a dry release test and aforce of 25±10 g/1.27 cm was required in a wet release test.

[0186] Brief Description of Test Methods Used in Examples

[0187] ASTMD1004-94a: This is a standard test method for initialtear-resistance of plastic film and sheeting. The test covers thedetermination of tear resistance of flexible plastic film and sheetingat very low rates (2 inches/min). The method is designed to measure theforce to initiate tearing. The specimen geometry of this test methodproduces a stress concentration in a small area of the specimen. Themaximum stress, usually found near the outset of tearing is recommendedas the tear resistance.

[0188] ASTMD1003: This is a standard test method for haze and luminoustransmittance of transparent plastics. The test covers the evaluation ofspecific light-transmitting and wide-angle-light-scattering propertiesof planar sections of materials, such as essentially transparentplastic. A hazemeter was used as mentioned in the earlier description ofthe haze test.

[0189] ASTMD1876: This is a standard test method for peel resistance ofadhesives (T-peel test). This test is primarily intended for determiningthe relative peel resistance of adhesive bonds between flexibleadherents.

[0190] ASTMD5946-99: This is a standard test method for corona treatedpolymer films using water contact angle measurements. The test coversmeasurement of the contact angle of water droplets on corona treatedpolymer film surface with subsequent estimation of the film's wettingtension.

[0191] Document #W-3020-641-02 from Morton International, Inc dated Jun.15, 1994 describes the technique used for determining the coating weight(lbs/ream) for adhesives and coatings. This method may be used fordetermining coating weights for hand lamination evaluation or fordetermining coatings weights from previously laminated samples.

[0192] The invention may be varied in any number of ways as would beapparent to a person skilled in the art and all obvious equivalents andthe like are meant to fall within the scope of this description andclaims. The description is meant to serve as a guide to interpret theclaims and not to limit them unnecessarily.

1. A release coating composition for polymer films, which films are for use in high temperature and/or high humidity applications, which composition comprises a solution of at least one hydroxypropyl methylcellulose having hydroxypropyl molar substitution of from 0 to about 0.82.
 2. A release coating composition as claimed in claim 1, wherein the solution comprises from about 0.2% to about 40% by weight of low viscosity hydroxypropyl methylcellulose having hydroxypropyl molar substitution of from 0 to about 0.82 in water, wherein low viscosity means the viscosity of a 2% by weight of a solution of hydroxypropyl methylcellulose in water at room temperature (20° C.) is up to 100 centipoise.
 3. A release coating composition as claimed in claim 1, wherein the solution comprises up to about 3% by weight of high viscosity hydroxypropyl methylcellulose having hydroxypropyl molar substitution of from 0 to about 0.82 in water, wherein high viscosity means the viscosity of a 2% by weight of a solution of hydroxypropyl methylcellulose in water at room temperature (20° C.) is from 100 to 100,000 centipoise.
 4. A release coating composition as claimed in claim 1, wherein the solution comprises from about 0.2% to about 40.0% by weight hydroxypropyl methylcellulose in water.
 5. A release coating composition as claimed in claim 1, wherein the solution comprises from about 0.2 to about 15% by weight of hydroxypropyl methylcellulose in water.
 6. A release coating composition as claimed in claim 1, wherein the solution comprises a mixture of non-aqueous solvent and water and the ratio of parts of solvent to hydroxypropyl methylcellulose ranges from about 2 to about 8:1.
 7. A release coating composition as claimed in claim 1, wherein the solution comprises from 0 to about 50% by weight of alcohol, from about 0.2% to about 6.0% by weight of hydroxypropyl methylcellulose, and the remainder up to 100% by weight is water.
 8. A release coating composition as claimed in claim 7, wherein from about 1% to about 35% by weight of alcohol is present.
 9. A release coating composition as claimed in claim 1, wherein a particulate solid is additionally present in the solution.
 10. A release coating composition as claimed in claim 9, wherein the particulate solid is silica.
 11. A release coating composition as claimed in claim 8, wherein the particulate solid is talc.
 12. A release coating composition as claimed in claim 6, wherein a particulate solid is additionally present in the solution.
 13. A release coating composition as claimed in claim 12, wherein the particulate solid is silica.
 14. A release coating composition as claimed in claim 12, wherein the particulate solid is talc.
 15. A release coating composition as claimed in claim 12, wherein the ratio of particulate solid to hydroxypropyl methylcellulose is in the range of from about 0.01 to about 1.5.
 16. A release coating composition as claimed in claim 15, wherein the solution comprises from 0 to about 50% by weight of organic solvent, from about 0.2% to about 15% by weight of hydroxypropyl methylcellulose, with the particulate solid present in the appropriate ratio, and the remainder up to 100% by weight is water.
 17. A release coating composition as claimed in claim 9, wherein the ratio of particulate solid to hydroxypropyl methylcellulose is in the range of from about 0.01 to about 1.5.
 18. A release coating composition as claimed in claim 1, wherein the polymer film is selected from the group comprising polyolefins, polyesters, nylons and combinations thereof.
 19. A release coating composition as claimed in claim 18, wherein the nylons are selected from Nylon66 and Nylon6 films.
 20. A release coating composition as claimed in claim 18, wherein the polymer film is monoaxially or biaxially oriented.
 21. A process for coating a surface of a polymer film with a release coating composition to provide a release film for use in high temperature and/or high humidity conditions, which comprises coating at least one surface of the polymer film with a solution of a hydroxypropyl methyl cellulose having hydroxypropyl molar substitution of from 0 to about 0.82 to provide a coating weight of at least about 0.004 lb/ream per side and drying the coated film to set the coating.
 22. A process as claimed in claim 21, wherein the film is coated on both sides in separate or single passes to achieve the desired coating weight.
 23. A release polymer film coated on at least one surface with hydroxypropyl methylcellulose having hydroxypropyl molar substitution of from 0 to about 0.82.
 24. A release polymer film as claimed in claim 23, wherein the coating weight is at least about 0.004 lb/ream per side.
 25. A release polymer film as claimed in claim 23, wherein the coating weight is at least about 0.2 lb/ream per side.
 26. A release polymer film as claimed in claim 23, wherein the film is coated with a mixture of the hydroxypropyl molar substitution of from 0 to about 0.82 and a particulate solid.
 27. A release polymer film as claimed in claim 26, wherein the particulate solid is silica.
 28. A release polymer film as claimed in claim 26, wherein the particulate solid is talc.
 29. A process for curing rubber which comprises forming a sheet rubber layer in a calendar, laying layers of a release substrate as claimed in claim 23 between layers of the sheet rubber, tightly overwrapping the stack of layers with a release film or cloth, before subjecting the stack of layers to elevated temperature in a dry or steam oven wherein the sheet rubber is cured and subsequently unwrapping the stacked, cured sheets.
 30. A process for curing rubber which comprises forming a sheet rubber layer in a calendar, laying layers of a release substrate as claimed in claim 26 between layers of the sheet rubber, tightly overwrapping the stack of layers with a release film or cloth, before subjecting the stack of layers to elevated temperature in a dry or steam oven wherein the sheet rubber is cured and subsequently unwrapping the stacked, cured sheets.
 31. A process for producing sheet molding composites which comprises: (a) casting a layer of heat-curable thermosetting resin, in fluid form, onto a continuously advancing polymeric release film; (b) introducing reinforcing material onto the advancing fluid layer; (c) laying a polymeric film on the top surface of said reinforced fluid layer thereby forming a sandwich composite; (d) advancing said sandwich composite through a series of kneading and compaction rolls; and (e) winding the sandwiched composite into a roll for partial curing; the improvement comprising using a release film as claimed in claim
 23. 32. A process for producing sheet molding composites which comprises: (a) casting a layer of heat-curable thermosetting resin, in fluid form, onto a continuously advancing polymeric release film; (b) introducing reinforcing material onto the advancing fluid layer; (c) laying a polymeric film on the top surface of said reinforced fluid layer thereby forming a sandwich composite; (d) advancing said sandwich composite through a series of kneading and compaction rolls; and (e) winding the sandwiched composite into a roll for partial curing; the improvement comprising using a release film as claimed in claim
 26. 33. A process for making thick molding composites, comprising (a) introducing reinforcing material into a heat-curable thermosetting resin, in fluid form and mixing same until the material is mixed and wetted; (b) casting a layer of said mixture onto a continuously advancing polymeric film; (c) laying a polymeric film on the top surface of said reinforcing material-resin layer to form a sandwich composite; (d) advancing the sandwich composite through at least one compaction roll; (e) cutting the continuous lengths of the sandwich composite into lengths for partial curing; the improvement comprising using a release film as claimed in claim
 23. 34. A process for making thick molding composites, comprising (a) introducing reinforcing material into a heat-curable thermosetting resin, in fluid form and mixing same until the material is mixed and wetted; (b) casting a layer of said mixture onto a continuously advancing polymeric film; (c) laying a polymeric film on the top surface of said reinforcing material-resin layer to form a sandwich composite; (d) advancing the sandwich composite through at least one compaction roll; (e) cutting the continuous lengths of the sandwich composite into lengths for partial curing; the improvement comprising using a release film as claimed in claim
 26. 